Which is the greatest 'witch hunt' in American history?

Speculation has been swirling that Alaska Gov. Sarah Palin has been selected as Sen. John McCain’s choice for running mate, giving him a force among women and younger voters. Palin has been credited with reforms in her state.

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DENVER | John McCain and other Republicans have been masterful this week at inserting themselves into Barack Obama’s Democratic National Convention, repeatedly stealing part of the limelight with hard-hitting ads, an aggressive effort to court disaffected Clinton supporters and tantalizing visits by possible Republican vice-presidential candidates.

Mr. McCain had narrowed his list to a handful of possibilities: Former rival Mitt Romney, Minnesota Gov. Tim Pawlenty, former Pennsylvania Gov. Tom Ridge and Alaska Gov. Sarah Palin, as well as wildcard Sen. Joe Lieberman, the Democrats’ 2000 vice-presidential nominee who is now an independent.

The nominee was to be called late Thursday and an announcement was set for Friday.

The mere suggestion that the name of the nominee might leak before or during Mr. Obama’s acceptance speech last night had top strategists playing defense during the day, firing off charges at any number of the possible selections.

The guessing game also kept the cable television networks busy, taking away from time that otherwise would have been devoted to covering Mr. Obama’s speech before 75,000 spectators in Denver.

Mr. McCain also released a commercial congratulating Mr. Obama, stealing yet more attention.

“How perfect that your nomination would come on this historic day. Tomorrow, we’ll be back at it. But tonight, Senator, job well done,” Mr. McCain said in the spot, referring to the anniversary Thursday of Martin Luther King’s “I Have a Dream” speech.

It was just the latest in a masterful manipulation of the press demonstrated by Mr. McCain and Republicans, who released daily Web videos and television commercials playing up a split between Mr. Obama and rival Hillary Rodham Clinton. Those were replayed repeatedly on cable news, earning television time that otherwise would have gone to Democrats.

“Note to Cable Networks: The only time McCain’s Clinton-themed ads are running is when they’re included in your programming,” Tommy Vietor, an Obama campaign spokesman, said in an e-mail fired off to reporters, citing a report that the McCain campaign has been giving the ads limited airtime, relying instead on news programs to give them play.

With his vice-presidential pick still to come, Mr. McCain has a chance to instantly suck the oxygen away from Mr. Obama and his convention speech.

He settled on his nominee Thursday and was scheduled to campaign with the pick Friday in Dayton, Ohio.

The senator from Arizona also plans to have several of those on his shortlist, such as Mr. Romney and Mr. Ridge, campaign with him in Pennsylvania on Saturday - part of a unity tour leading up to next week’s Republican National Convention in St. Paul, Minn.

Some delegations at the Republican convention signaled they would either vote against Mr. Lieberman’s nomination or walk out of the convention.

Meanwhile, Sen. Kay Bailey Hutchison, Texas Republican, told Fox News that she is not in the running and said she expects the pick to be Mr. Romney.

Playing defense Thursday morning, Obama campaign manager David Plouffe and chief strategist David Axelrod previewed their lines of attack for some of Mr. McCain’s choices.

“Whoever he picks doesn’t change the fact that it’s John McCain’s agenda on the ballot,” Mr. Plouffe said. “If you liked the last eight years … he’s going to give you more of the same Bush economic policies.”

If he chooses Mr. Romney, “all he’s done is sort of double down on out of touch, and being on the side of the big corporate special interests,” Mr. Plouffe said. “Romney’s an expert on things like Cayman Islands tax shelters.”

Mr. Axelrod suggested that Mr. McCain has sold out to conservatives in his party by appearing to back away from naming a pro-choice running mate.

“You’ve seen … basically people in his party holding a gun to his head and saying you cannot pick a pro-choice candidate and setting the parameters of this,” he said. “He’s not been fully embraced by conservatives in the party and now he’s not really trusted by moderates either because he’s made this Faustian bargain to be the nominee of the Republican Party.”

Mr. Pawlenty, in Denver to headline the Republicans’ response for the day, told reporters he planned to be at Minnesota’s state fair Friday, rather than campaigning with Mr. McCain in Ohio.

But his performance at the press conference made it clear he thought he was still in the running.

Despite the presence of other top Republicans, Mr. Pawlenty fielded most of the questions, aiming the kinds of barbs at Mr. Obama that a running mate is expected to fire.

He also did not shy away from listing the credentials that could make him an acceptable vice president: six years as governor, and before that state Senate majority leader. And he noted that being governor means being commander in chief of Minnesota’s National Guard.

• Ralph Z. Hallow, reporting from Minneapolis, Christina Bellantoni in Denver, and Joseph Curl, traveling with the McCain campaign, contributed to this article.